Protect against image conversion failure in mac::FaviconForTabContents().

chrome/browser/ui/cocoa/tab_contents/favicon_util.mm

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/cocoa/tab_contents/favicon_util.h"
 
 #import <AppKit/AppKit.h>
 
 #include "app/mac/nsimage_cache.h"
 #include "base/mac/mac_util.h"
 #include "content/browser/tab_contents/tab_contents.h"
 #include "skia/ext/skia_utils_mac.h"
 
 namespace mac {
 
 NSImage* FaviconForTabContents(TabContents* contents) {
   // TabContents returns IDR_DEFAULT_FAVICON, which is a rasterized version of
   // the Mac PDF. Use the PDF so the icon in the Omnibox matches the default
   // favicon.
   if (contents && contents->FaviconIsValid()) {
     CGColorSpaceRef color_space = base::mac::GetSystemColorSpace();
-    return gfx::SkBitmapToNSImageWithColorSpace(contents->GetFavicon(),
-                                                color_space);
+    NSImage* image =
+        gfx::SkBitmapToNSImageWithColorSpace(contents->GetFavicon(),
+                                             color_space);
+    // The |image| could be nil if the bitmap is null. In that case, fallback
+    // to the default image.
+    if (image) {
+      return image;
+    }
   }
 
   return app::mac::GetCachedImageWithName(@"nav.pdf");
 }
 
 }  // namespace mac